1. Field of the Invention
In a signal processing apparatus configured to perform signal processing based on image data and an image forming apparatus, the present invention relates to a technique to cancel a difference of the actual value and the ideal value of an image creating signal.
2. Description of Related Art
In an apparatus well known as an image forming apparatus, image creating signals are produced in accordance with image data, images are formed on one line or several lines in the main scanning direction based on the image creating signals, and the image formation on each line in the main scanning direction is repeated in the subsidiary scanning direction, whereby image formation for one page is performed.
In an electro-photographing type image forming apparatuses being one example of the above apparatus, image creating signals are produced from image data. PWM signals produced by a PWM circuit correspond to such image creating signals. In such an image forming apparatus, a laser beam modulated based on the PWM signals is made to scan in a main scanning direction, and in parallel to the scanning in the main scanning direction, an image carrying member is rotated in the subsidiary scanning direction. Accordingly, on the image carrying member, a two dimensional image is formed by the laser beam.
Incidentally, due to environmental factors, such as a temperature change, and various factors such as individual differences of circuit elements, image creating signals, such as PWM signals cause fluctuation in signal width. That is, the measured actual signal width (actual value) of an image creating signal may become a different value from a signal width (ideal value) which is originally planned. The fluctuation of the actual value of the image creating signal causes density level changes on images formed by the image forming apparatus.
In the image forming apparatus, the positioning of image formation in the main scanning direction in response to image data is made on the basis of clocks which are used as a standard of pixels to be formed and called “image processing clock” or “dot clock”.
Techniques with regard to correction of such a density level change in the image forming apparatus are disclosed in Patent Documents, such as Japan Unexamined Patent Publication Nos. 2002-244407, 11-196273, and 8-156330.